The present invention relates generally to data communications. More specifically, the Present invention relates to an interface between the 1394 standard and the Ethernet standard.
When discussing data communications in general, it can be useful to refer to a model. In an attempt to bring a level of standardization between protocols, the International Standards Organization (ISO) developed the Open Systems Interconnect Model (OSI Model). The model is intended to illustrate the separable functions needed for data communication among computers and devices. The Model is helpful in understanding the data communication process in terms of functions operating at separate layers. Each layer plays a role in getting the data between the source and destination. Although the OSI Model involves seven separate layers, it is true that certain network communication protocols do not share this view. Instead, each protocol may have its own view on the number of layers and the function of each. Nevertheless, a brief review of the OSI Model will be useful as background material.
At the bottom is the physical layer. The physical layer defines the electrical characteristics of the actual connection between network nodes. The next layer up, the data link layer, deals with how the network is shared between nodes. One popular set of standards defines the data link layer as including two levels: the Media Access Control (MAC) level, which sets rules covering when each node on the network can send messages; and the Logical Link Control (LLC) level, which provides a connection-oriented service between nodes.
Next layer up is the network layer which provides routing; it provides addressing information to guide data through the network. The top four layers (4th through 7th) concern network architecture. The fourth layer, the transport layer, is concerned with end-to-end message transport across the network. The next three layers are related to applications. The session layer is concerned with establishing the commencement and completion of a session between applications. The presentation layer is used to insure that users view incoming information in a set format. Finally, application layer seven is concerned with the interface between the network and the application. Thus, the OSI Model defines an architecture having seven layers: it does not, however, provide or define protocols. Protocols can be established that conform to the OSI Model if desired.
Further relevant background regarding the 1394 standard will now be provided. The 1394 standard set forth by IEEE for implementing the physical, data link and network layers has recently become popular. Original known as FIREWIRE, 1394 is a set of protocols designed for smaller networks, and has been termed a xe2x80x9cdesktop area network.xe2x80x9d For example, in a network using 1394, nodes are typically no more than 4xc2xd meters apart and the network is no more than 72 meters in diameter in total. Devices that might have a 1394 interface include digital camcorders, computers, televisions, digital recorders, DVD players, video game consoles, etc. These devices may be connected to one another point-to-point to form a network using the 1394 standard.
Although the 1394 standard is now being used, it does have inherent limitations. It would be desirable to have methods and apparatus that would overcome some of the inherent limitations in the 1394 standard, such as its communication distance, while at the same time providing a more reliable standard.
To achieve the foregoing, and in accordance with the purpose of the present invention, an interface device is disclosed that provides communication between a 1394 controller and an Ethernet transceiver.
The present invention is advantageous because it allows devices using the 1394 standard to communicate at distances of up to 100 meters by taking advantage of the Ethernet standard. Essentially, the 1394 standard is able to be implemented over Ethernet. By taking advantage of available, inexpensive, and tested Ethernet transceivers, the speed of 1394 is also improved. The present invention allows speeds of from 100 Mbps up to 800 Mbps. Thus, high-speed 1394 applications can be implemented over greater distances using traditional copper twisted-pair wiring. There is an effort underway termed FIBERCHANNEL that seeks to implement 1394 over greater distances, but it must be implemented using fiber optics, and currently has only a top speed of 100 Mbps.
The interface device of the present invention thus allows the interoperation of an IEEE 1394 link layer device with an IEEE 802.3 physical layer device (commonly called a xe2x80x9cPHYxe2x80x9d). Because these devices were designed for different applications, have different physical interfaces, and operate at different speeds, the interface device provides conversion and emulation to accommodate the two different standards. For example, there are clocking differences to be resolved, data speed differences to be managed, and management requirements to be fulfilled.
To address the clocking issues, the interface device uses two clocks to supply timing clocks for the link (as would a 1394 PHY) and the PHY (as would a 802.3 MAC). For speed matching, the interface device matches the data rate of the link (S100, S200, S400, S800) with the PHY (nominally 1 Gbps) using a padding algorithm. The interface device provides the link with management information through a set of IEEE 1394 compatible registers that are accessed through the 1394 interface, emulating a single port 1394 PHY. The interface device also manages the IEEE 802.3 PHY as would a MAC through the MDC/MDIO interface.